Electrical expansion joint and system using same

ABSTRACT

An expansion joint having a pair of spaced supports which are adapted to be fixed to associated ends of a pair of electrical conductors and the expansion joint is provided with a plurality of flexible electrical leads having their opposite ends fastened to the spaced supports. Means is provided for rotating the central portions of the leads to take up varying amounts of slack therein caused by relative movement of the supports toward and away from each other.

United States Patent [72] inventors George F. Swenck;

John J. Bahen, Jr.; Robert B. Lightner, all of Richmond. Va. [21] Appl.No. 864,438 [22]. Filed Oct. 7,1969 [45] Patented July 6, 1971 {73]Assignee Reynolds Metals Company Richmond, Va.

{ 54] ELECTRICAL EXPANSION JOINT AND SYSTEM USING SAME 20 Claims, 7Drawing Figs.

[52] US. Cl 174/13, 174/15 C, 174/21 C, 174/28, 174/99 E [51] Int.ClHOlb 9/04, H02g 15/24 [50] Field of Search 174/12 R,

13, 15C,16B,21 R,21C,21CA,22R,22C,27, 28,29, 86,88 R, 88 B, 88 C,99 R,99 B, 99 E; 339/1 R, 8 R, 9 E", 285/223, 298

[56] References Cited UNITED STATES PATENTS 409,183 8/1889 De Ferranti174/86 2,306,527 12/1942 Daniels 174/12 UX 3,325,588 6/1967 Lear 174/99(B) X Primary ExaminerLaramie E. Askin Att0rneyGlenn, Palmer, Lyne,Gibbs & Thompson ABSTRACT: An expansion joint having a pair of spacedsupports which are adapted to be fixed to associated ends of a pair ofelectrical conductors and the expansion joint is provided with aplurality of flexible electrical leads having their opposite endsfastened to the spaced supports; Means is provided for rotating thecentral portions of the leads to take up varying amounts of slacktherein caused by relative movement of the supports toward and .awayfrom each other.

PATENIEU JUL SIB?! 359L703 SHEEI 2 BF 2 INVENTORS SWENCK JOHN J. BAHENJR. BY ROBERT B. LIGHTNER THElR ATTORNEYS ELECTRICAL EXPANSION JOINT ANDSYSTEM USING SAME BACKGROUND OF THE INVENTION Electrical powertransmission conductors used to transmit electrical power over greatdistances are subject to a wide range of temperatures causing largeexpanding and contracting movements thereof. In underground systems, forexample, the conductors must be supported laterally in an electricallyinsulated manner within confined limits and such conductors expand andcontract comparatively large amounts along their length. In particular,the typical change in length in a 40-foot length of a 230 kv.transmission system due to current fiow may be generally of the order ofone-half inch and is produced by a temperature change of approximately80 C. and under overload conditions greater temperature changes resultin length changes approaching 1 inch in each 40-foot length. Therefore,it is necessary to provide means for compensating for the large amountsof expansion and contraction by either system design or providingsuitable expansion joints, or the like. In using one or more expansionjoints in a system wherein the conductors are housed in a protectiveconduit it is desirable that each expansion joint be of minimum size sothat it may be housed within such conduit with maximum space between theexpansion joint and protective conduit; and, it is also desirable thatthe expansion joint be constructed so that it does not increase indiameter or cross'sectional outline during expanding and contractingmovements thereof.

SUMMARY This invention provides an improved expansion joint andelectrical power transmission system using same wherein such expansionjoint is of substantially cylindrical configuration and has across-sectional peripheral outline which remains leads having theiropposite ends fastened to the spaced supports with means being providedto rotate a central portion of the leads to take up varying amounts ofslack therein caused by relative movement of the supports toward andaway from each other.

Other details, uses, and advantages of this invention will becomeapparent as the following description of the exemplary embodimentsthereof presented in the accompanying drawings proceeds.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings show presentexemplary embodiments of this invention, in which FIG. 1 is a view withparts in cross section and parts broken away illustrating a plurality ofexpansion joints of this invention suitably fastened in position toassociated ends of elongated electrical conductors, with the conductorsand expansion joints being carried within an associated protectiveconduit to define a portion of a housed electrical power transmissionsystem;

FIG. 2 is a greatly enlarged view taken essentially on the line 2-2 ofFIG. 1 with parts in cross section and parts broken away;

FIG. 3 is a view taken essentially on the line 33 of FIG. 2

FIG. 4 is a perspective view with parts broken away of the exemplaryexpansion joint illustrated in FIG. 1 fastened between an associatedpair of electrical conductors and showing a plurality of flexibleelectrical leads comprising the expansion joint in a straight condition;

FIG. 5 is a perspective view similar to FIG. 4 and particularlyillustrating opposed end supports of the expansion joint of FIG 1 movedtoward each other due to expansion of an associated pair of electricalconductors toward each other and illustrating the manner in whichrotating means comprising the expansion joint take up slack in theelectrical leads due to such expansion;

FIG. 6 is a fragmentary, perspective view similar to the lefthandportion of the view illustrated in FIG. 5 and illustrating anotherexemplary embodiment of the expansion joint of this invention; and

FIG. 7 is a cross-sectional view taken essentially on the line 7-7 ofFIG. 6.

DESCRIPTION OF ILLUSTRATED EMBODIMENTS Reference is now made to FIG. 1of the drawings wherein one exemplary embodiment of an electrical powertransmission' system of this invention is illustrated and designatedgenerally by the reference numeral 20. The power transmission system maybe used in any application where it is desired to transmit electricalpower through housed or protected con ductors and comprises an outerprotective conduit or housing which is designated generally by thereference numeral 21 and is comprised of a plurality of substantiallycylindrical conduit sections 22 suitably fixed together in end-to-endrelation so as to provide a fluidtight connection between adjoiningsections. In this example of the invention adjoining conduit sections 22are fixed together by welding at a plurality of locations eachdesignated by the reference numeral 23.

The exemplary electrical system 20 comprises a plurality of elongatedtubular electrical conductors 24 which in this example of the inventionhave a right circular cylindrical outer configuration. However, it willbe appreciated that the conductors 24 used in system 20 may have anydesired peripheral outline as vfewed in cross section and may be ofsolid rather than of tubular construction and selected ones of theconductors 24 are suitably fixed together in end-to-end relationutilizing one exemplary embodiment of the expansion joint of thisinvention which is designated generally by the reference numeral 25.

The expansion joint 25 may be installed in position at any desiredlocation along the length of the electrical power transmission system 20and is utilized to compensate for expanding and contracting movements ofassociated electrical conductors 24. The expansion joint 25 is ofcomparatively small peripheral outline as viewed in cross section, seeFIGS. 1-3, which enables it to be used in the electrical powertransmission system 20 without providing enlarged portions in thehousing 21 and the unique construction of the expansion joint 25 is suchthat during expanding and contracting movements thereof its peripheraloutline as viewed in cross section remains substantially constant andonce the expansion joint 25 has been installed in' position it is notnecessary to be concerned with a change in size thereof and particularlywith an increase in peripheral outline due to expansion of an associatedpair of conductors 24 between which such expansion joint is installed,whereby the expansion joint 25 assures that a safe distance indicated at26 is maintained between the entire outer periphery of such expansionjoint and the inside surface of the housing 21 upon suitably supportingthe conductors 24 and expansion joints 25 within the protective housing21.

The conductors 24 are supported substantially centrally withinprotective conduit 21 by a plurality of insulating spacers 30 and eachspacer 30 is made of a suitable electrical insulating material. Eachspacer 30 is attached to its associated electrical conductor 24 usingany suitable technique such as welding, adhesive means, or spotweldingannular bands or lugs in position against an associated portion of thetubular conductor 24 so as to prevent axial movement of spacer 30relative to its associated conductor. As seen in FIG. 2 of the drawings,each spacer 30 of this example is shown held in its axial position byannular beads 31 welded against the associated conductor 24 on oppositesides thereof.

The power transmission system preferably utilizes an electricallynonconductive (i.e electrical insulating) fluid such as an inert gas.for example. under pressure which is carried within the protectiveconduit 21 so that it fills the volume between each conductor 24 andexpansion joint 25 and the outer housing 21. The use of an inert gas,indicated by the reference numeral 32 in FIGS. 1 and 2. under pressure,helps to assure the provision of optimum electrical insulation along thefull length of each electrical conductor 24 and expansion joint 25 andsuch inert gas also serves to dissipate heat away from the conductors 24and expansion joints 25 to help provide more efficient cooling of thesecomponents. Further, each insulating spacer has a plurality of openings33 provided therein in any desired pattern to enable unobstructed flowof the inert gas along the full length of the protective conduit 21.

As seen particularly in FIGS. 4 and 5 of the drawings, each expansionjoint 25 comprises a pair of spaced supports or end plates 34 ofcircular peripheral outline and each plate 34 is adapted to be fixed toan associated one of the electrical conductors 24 and in a manner to besubsequently described. The expansion joint 25 has a plurality offlexible electrical leads 35 which have their opposite ends 36 and 37fastened to the spaced support plates 34.

The expansion joint 25 has means for rotating a central portion of theleads 35 to take up varying amounts of slack therein caused by relativemovement of the plates 34 and such rotating means is indicated generallyby the reference numeral 40. The rotating means 40 comprises a rotatablecentral member or circular disc 41 which has a plurality of peripheralcutouts 42 provided therein and each cutout has a cross-sectionaloutline which corresponds to the cross-sectional outline of anassociated lead 35. A central portion 43 of each lead 35 is placedwithin an associated cutout 42 and attached to the disc 41 as by weldingor other suitable means.

The rotating means 40 also comprises an elongated member in the form ofa rod 44 which in this example is of right circu larcylindrical-configuration and the rod 44 has one end 45 suitably fixedto one of the end plates 34. The oppositely arranged end plate 34 has aright circular cylindrical surface 46 which defines an opening 50extending therethrough and the opposite end 51 of the rod 44 extendsthrough the opening 50 and is supported by the cylindrical surface 46.The diameter of cylindrical surface 46 is such that the end portion 51of rod 44 slides through opening 50 in an unobstructed manner withmovement of end plates 34 toward and away from each other yet surface 46supports end portion 51 of rod 44 in a direction perpendicular to itslongitudinal axis. The circular disc 41 also has a right circularcylindrical surface 52 which defines a central opening 53, see FIG. 2,extending centrally therethrough and the rod 44 extends through opening53 so that surface 52 rotatably supports the disc 41 on rod 44.

The rotating means 40 also comprises a spring device in the form of atorsion spring 54 which has one end 55 suitably fixed to the rod 44 andits opposite end 56 is suitably fixed to the disc 41 adjacent the outerperiphery thereof whereby the torsion spring 54 constantly tends torotate the disc 41 about the rod 44. As the associated ends of theconductors 24 move toward each other due to expansion it will beappreciated that a substantial amount of slack will be provided in theelectrical leads 35 comprising the expansion joint 25. The torsionspring 54 being in a constantly coiled condition tends to rotate thecircular disc 41 counterclockwise, as viewed from left to right in FIG.5, to thereby take up the slack caused by movement of the end plates 34toward each other and essentially as indicated at 57.

The electrical leads 35 have their opposite ends each fixed to anassociated plate 34 on a given diameter and with each end of a lead 35being received within an associated peripheral slot 59 in an associatedplate 34. In this example of the invention the plates 34 are of equaldiameter, indicated at 60, and the associated ends (36 or 37) of leads35 are fixed in position with their outer surface portions substantiallycoinciding with the outside diameter of an associated end plate 34. Thecentral disc 41 of this example also has the same outside diameter asthe plates 34 and it will be seen that during expansion of the tubularconductors 24, from the position of FIG. 4 to the position of FIG. 5,for example, the end plates 34 move toward each other, which wouldordinarily cause slack to be provided in the leads 35. However, torsionspring 54 rotates the disc 41 about rod 44 to maintain the leads 35within the confines of a theoretical cylindrical boundary extendingbetween the support plates 34 and such boundary could be visualized ashaving a diameter substantially equal to the diameter 60.

The expansion joint 25 is illustrated in FIG. 4 with the electricalleads in a straight condition, for simplicity. However, it will beappreciated that in an actual installation such expansion joint would beinitially installed in position between a pair of associated electricalconductors 24 so that there would be a slight amount of slack in theconductors 35 whereby the disc 41 would be in a slightly rotatedposition somewhere between the position indicated in FIG. 4 and theposition illustrated in FIG. 5. By installing the expansion joint insuch a slightly rotated position it will be appreciated that bothexpanding and contracting movements could be compensated for so that inthe event of contraction of the conductors 24 due to environmentalconditions the tendency would be for movement of the plates 34 away fromeach other whereby the electrical leads 35 would then tend to straightentoward the position illustrated in FIG. 4. 1

Certain ones of the conductors 24 are preferably confined to preventaxial movement thereof within the protective housing 21 and thus preventcreeping of the conductors 24 and expansion joints 25 within housing 21.In this example of the invention, certain selected ones of the spacers30 are confined by a pair of annular rings 61, see FIGS. 1 and 2, whichare arranged on opposite sides of the associated spacer 30 and each ringis welded to an associated section 22 of the outer housing 21 by anassociated weld 62.

The expansion joint 25 may be suitably fixed between the ends of anassociated pair of electrical conductors 24 in any suitable manner;however, in this example of the invention a substantially frustoconicaltubular transition section 63 is utilized, as seen in FIG. 2, with thesmall-diameter end thereof welded to an associated tubular conduit 24 bya weld 64 and the large-diameter end thereof welded to an associated endplate 34 by a weld 65.

Each lead 35 comprising the expansion joint 25 may be comprised of aplurality of individual strands shown as elongated thin metal strips 66of rectangular cross-sectional outline, see FIG. 3, having a width whichis substantially greater than the thickness thereof. Each strip 66 isarranged substantially on edge with its wide surfaces arrangedsubstantially parallel to parallel lines radiating from a central axisthrough the expansion joint 25 whereby the strips 66 offer minimumresistance to rotation by the rotating means 40.

Another exemplary embodiment of this invention is illustrated infragmentary perspective view in FIG. 6 of the drawings. The expansionjoint illustrated in FIG. 6 is very similar to the expansion joint 25;therefore, such expansion joint will be designated generally by thereference numeral 25A and parts of the expansion joint 25A which arevery similar to corresponding parts of the expansion joint 25 will bedesignated by the same reference numeral as the expansion joint 25 alsofollowed by the letter designation A and not described again. Only thosecomponent parts of the expansion joint 25A which are substantiallydifferent from corresponding parts of the expansion joint 25 will bedesignated by a new reference numeral also followed by the letterdesignation A and described in detail.

The main difference between the expansion joint 25 and 25A is that inthe expansion joint 25A the end plates 34A are approximately equal inoutside diameter to the outside diameter of the tubular electricalconductors 24 and the rotating means 40A has an elongated rod 70A whichhas an end 71A fixed, to one end plate 34A in a substantiallycantilevered manner with the length of the rod 70A being such that itextends only a short distance beyond the center of the expansion jointA. In addition, each lead 35A comprising the expansion joint 25A iscomprised of a plurality of individual wires or strands 72A, see FIG. 7,each of circular cross-sectional outline which are suitably arranged ina bundle to define the lead 35A and if desired the wires may be twistedtogether. The opposite ends 36A and 37A of the leads 35A are suitablyfixed to their associated end plates 34A, as by welding, to provide ahigh-quality mechanical and electrical connection.

Each circular end plate 34A may be welded directly to an adjoiningconductor 24 by an annular weld as indicated at 73A. However, a suitabletransition member such as a tubular member or solid flat disc may beinterposed and welded between the end of a conductor 24 and anassociated end plate 34A.

In this disclosure of the invention the electrical leads 35 comprisingthe expansion joint 25 are shown as being comprised of a plurality offlat strips 66 and the rod 44 of such expansion joint extends the fulllength thereof between associated end plates 34. However, it will beappreciated that each lead 35 may be comprised of a plurality ofindividual strands of either noncircular or circular cross-sectionalconfiguration and the rod 44 need not necessarily extend the full lengthof the expansion joint 25 but may extend roughly onehalf the lengththereofin a similar manner as the rod 70A illustrated in the expansionjoint 25A, Likewise, the expansion joint 25A may have its rod 70Aextending the full length thereof and the individual strands or wires72A comprising each lead 35A may be of any desired cross-sectionalconfiguration.

lrrespective of the particular cross-sectional configuration andarrangement of its leads, the expansion joint of this invention enablesexpanding and contracting movements of adjoining electrical conductorswhile the outside diameter of such expansion joint remains substantiallyconstant thereby assuring trouble-free operation. ln addition, it willbe seen that optimum controlled spacing is maintained between theelectrical leads of each expansion joint irrespective of the amount ofrelative movement between the associated end plates whereby there ispractically no chance of arcing between adjacent electrical leads. Itwill also be appreciated that the construction of the expansion joint ofthis invention is such that it may be easily provided with a suitableanticorona electrical discharge shield, if desired.

Electrical conducting materials of all types may be utilized to make theconductors 24 and expansion joints 25 comprising the system 20. Metallicmaterials containing aluminum are preferred in many applications and ina typical 230 kv. electrical transmission system the conductors 24 maybe in the form of tubular conductors made of 6l0l-T64 aluminum alloy andhaving a 4-inch outside diameter and a re-inch wall thickness Whilepresent exemplary embodiments of this invention, and methods ofpracticing the same, have been illustrated and described, it will berecognized that this invention may be otherwise variously embodied andpracticed by those skilled in the art.

What we claim is:

1. An expansion joint for electrically connecting associated ends of apair of electrical conductors comprising, a pair of spaced supports eachadapted to be fixed to an associated one of said electrical conductors,a plurality of flexible electrical leads having their opposite endsfastened to said spaced supports, and means engaging and rotating acentral portion of each lead relative to both of its opposite ends totake up any slack therein caused by relative axial movement of saidsupports.

2. An expansion joint for electrically connecting associated ends of apair of electrical conductors comprising, a pair of spaced supports eachadapted to be fixed to an associated one of said electrical conductors,a plurality of flexible electrical leads having their opposite endsfastened to said spaced supports, and means rotating a central portionof said leads to take up any slack therein caused by relative movementof said supports, said rotating means comprising a central member havinga central portion of each lead attached thereto and a spring deviceacting between at least one support and said central member, said springdevice yieldingly rotating said central member to thereby rotate thecentral portion of each lead to take up any slack therein.

3. An expansion joint as set forth in claim 2 in which said springdevice comprises a torsion spring.

4. An expansion joint for electrically connecting associated ends of apair of electrical conductors comprising, a pair of spaced supports eachadapted to be fixed to an associated one of said electrical conductors,a plurality of flexible electrical leads having their opposite endsfastened to said spaced supports, and means rotating a central portionof said leads to take up any slack therein caused by relative movementof said supports, said rotating means comprising an elongated memberhaving an end portion fixed to one of said supports, a central membersupported for unobstructed rotation about said elongated member, saidcentral member having a central portion of each lead attached theretoand a spring device acting between said elongated member and centralmember to yieldingly rotate said central member about said elongatedmember and thereby rotate the central portion of each lead to take upany slack therein.

5. An expansion joint as set forth in claim 4 in which each of saidelectrical leads is comprised of a plurality of individual strandsarranged in a bundle.

6, An expansion joint for electrically connecting associated ends ofapair of electrical conductors comprising, a pair of spaced supports eachadapted to be fixed to an associated one of said electrical conductors,a plurality of electrical leads having their opposite ends fixed to saidspaced supports with each end being fixed to an associated support on agiven diameter, and means engaging and rotating a central portion ofeach lead relative to both of its opposite ends to take up any slacktherein caused by relative axial movement of said supports to keep saidleads within the confines of a theoretical cylindrical boundaryextending between said supports and having said given diameter.

7. An expansion joint as set forth in claim 6 in which each of said pairof electrical conductors has a circular outline with a diameter equal tosaid given diameter and each of said supports comprises a circular platehaving an outside diameter also approximately equal to said givendiameter.

8. An expansion joint for electrically connecting associated ends of apair of electrical conductors comprising, a pair of spaced supports eachadapted to be fixed to an associated one of said electrical conductors,a plurality of electrical leads having their opposite ends fixed to saidspaced supports with each end being fixed to an associated support on agiven diameter, and means rotating a central portion of said leads totake up any slack therein caused by relative movement of said supportsto keep said leads within the confines of a theoretical cylindricalboundary extending between said supports and having said given diameter,said rotating means comprising a central circular disc having an outsidediameter equal to said given diameter and having the central portions ofsaid leads fixed to the outer periphery thereof at spaced intervals anda spring device acting between at least one support and said centraldisc, said spring device yieldingly rotating said central disc tothereby rotate the central portion of each lead to take up any slacktherein while keeping said leads within said cylindrical boundary.

9. An expansion joint for electrically connecting associated ends of apair of electrical conductors comprising, a pair of spaced supports eachadapted to be fixed to an associated one of said electrical conductors,a plurality of electrical leads having their opposite ends fixed to saidspaced supports with each end being fixed to an associated one of saidelectrical conductors, a plurality of electrical leads having theiropposite ends fixed to said spaced supports with each end being fixed toan associated support on a given diameter, and means rotating a centralportion of said leads to takeup any slack therein caused by relativemovement of said supports to keep said leads within the confines of atheoretical cylindrical boundary extending between said supports andhaving said given diameter, each of said supports having a circularperipheral outline and a diameter equal to said given diameter, witheach end of said leads being fixed to an associated support about itsperipheral outline to define said expansion joint having a roughlycylindrical configuration of constant diameter which corresponds to saidtheoretical cylindrical boundary, said rotating means comprising acentral circular disc having an outside diameter equal to said givendiameter and having the central portions of said leads fixed to theouter periphery thereof at spaced intervals and a spring device actingbetween at least one support and said central disc, said spring deviceyieldingly rotating said central disc to thereby rotate the centralportion of each lead to take up any slack therein while maintaining saidcylindrical configuration of said expansion joint substantially intact.

10. An expansion joint as set forth in claim 9 in which said rotatingmeans further comprises a rod having one end portion fixed to one ofsaid supports and its opposite end portion supported by the othersupport for sliding movement relative thereto, said central disc beingrotatably supported by said rod and said spring device acting betweensaid rod and central disc to rotate said disc and said central portionof each lead.

11. An expansion joint as set forth in claim 10 in which said rodcomprises a right circular cylindrical rod and said central disc has aright circular cylindrical inside surface extending through the centerthereof which defines an opening for receiving said rod, saidcylindrical surface supporting and enabling free rotation of saidcentral disc about said rod.

12. An expansion joint as set forth in claim 10 in which said springdevice comprises a torsion spring and each of said electrical leads iscomprised of a plurality of individual strands arranged in a bundle.

13. An electrical power transmission system comprising; an outerprotective conduit; a plurality of elongated electrical conductorssupported in electrically insulated relation within said conduit; and anexpansion joint for electrically connecting associated ends of anadjacent pair of said elongated conductors supported within saidconduit; said expansion joint comprising, a pair of spaced supports eachfixed to an associated one of said electrical conductors, a plurality ofelectrical leads having their opposite ends fixed to said spacedsupports with each end being fixed to an associated support on a givendiameter, and means engaging and rotating a central portion of each leadrelative to both of its opposite ends to take up any slack thereincaused by relative axial movement of said supports to keep said leadswithin the confines of a theoretical cylindrical boundary extendingbetween said supports and having said given diameter.

14. A system as set forth in claim 13 and further comprising a pluralityof disclike electrical insulating spacers each fixed concentricallyaround an associated electrical conductor and each supporting anassociated conductor within said conduit.

15. A system as set forth in claim 14 in which each of said spacers hasa plurality of passages extending therethrough and said system furthercomprising an electrical insulating fluid contained within said conduitunder pressure and filling the volume between each electrical conductorand expansion joint and said conduit, said electrical insulating fluidbeing free to flow through said passages to provide improved insulationand cooling along the full length of each electrical conductor and anyassociated expansion joint.

16. A system as set forth in claim 13 in which each of said pair ofelectrical conductors has a circular outline with a diameter equal tosaid given diameter and each of said supports comprises a circular platehaving an outside diameter also approximately equal to said givendiameter.

17. An electrical power transmission system comprising; an

outer protective conduit; a plurality of elon ated elect ric alconductors supported in electrically insulate relation within saidconduit; and an expansion joint for electrically connecting associatedends of an adjacent pair of said elongated conductors supported withinsaid conduit; said expansion joint comprising; a pair of spaced supportseach fixed to an associated one of said electrical conductors, aplurality of electrical leads having their opposite ends fixed to saidspaced supports with each end being fixed to an associated support on agiven diameter, and means rotating a central portion of said leads totake up any slack therein caused by relative movement of said supportsto keep said leads within the confines of a theoretical cylindricalboundary extending between said supports and having said given diameter,each of said supports having a circular peripheral outline and adiameter equal to said given diameter with each end of said leads beingfixed to an associated support about its peripheral outline to definesaid expansion joint having a roughly cylindrical configuration ofconstant diameter which corresponds to said theoretical cylindricalboundary, said rotating means comprising a central circular disc havingan outside diameter equal to said given diameter and having the centralportions of said leads fixed to the outer periphery thereof at spacedintervals and a spring device acting between at least one support andsaid central disc, said spring device yieldingly rotating said centraldisc to thereby rotate the central portion of each lead to take up anyslack therein while maintaining said cylindrical configuration of saidexpansion joint substantially intact.

18. A system as set forth in claim 17 in which said rotating meanscomprises a rod having one end portion fixed to one of said supports andits opposite end portion supported by the other support for slidingmovement relative thereto, said central disc being rotatably supportedby said rod and said spring device acting between said rod and centraldisc to rotate said disc and said central portion of each lead.

19. A system as set forth in claim 18 in which said rod comprises aright circular cylindrical rod and said central disc has a rightcircular cylindrical surface through the center thereof which defines anopening for receiving said rod, said cylindrical surface supporting andenabling free rotation of said central disc about said rod.

20. A system as set forth in claim 18 in which said spring devicecomprises a torsion spring and each of said electrical leads iscomprisedof a plurality of individual strands arranged in a bundle.

1. An expansion joint for electrically connecting associated ends of apair of electrical conductors comprising, a pair of spaced supports eachadapted to be fixed to an associated one of said electrical conductors,a plurality of flexible electrical leads having their opposite endsfastened to said spaced supports, and means engaging and rotating acentral portion of each lead relative to both of its opposite ends totake up any slack therein caused by relative axial movement of saidsupports.
 2. An expansion joint for electrically connecting associatedends of a pair of electrical conductors comprising, a pair of spacedsupports each adapted to be fixed to an associated one of saidelectrical conductors, a plurality of flexible electrical leads havingtheir opposite ends fastened to said spaced supports, and means rotatinga central portion of said leads to take up any slack therein caused byrelative movement of said supports, said rotating means comprising acentral member having a central portion of each lead attached theretoand a spring device acting between at least one support and said centralmember, said spring device yieldingly rotating said central member tothereby rotate the central portion of each lead to take up any slacktherein.
 3. An expansion joint as set forth in claim 2 in which saidspring device comprises a torsion spring.
 4. An expansion joint forelectrically connecting associated ends of a pair of electricalconductors comprising, a pair of spaced supports each adapted to befixed to an associated one of said electrical conductors, a plurality offlexible electrical leads having their opposite ends fastened to saidspaced supports, and means rotating a central portion of said leads totake up any slack therein caused by relative movement of said supports,said rotating means comprising an elongated member having an end portionfixed to one of said supports, a central member supported forunobstructed rotation about said elongated member, said central memberhaving a central portion of each lead attached thereto and a springdevice acting between said elongated member and central member toyieldingly rotate said central member about said elongated member andthereby rotate the central portion of each lead to take up any slacktherein.
 5. An expansion joint as set forth in claim 4 in which each ofsaid electrical leads is comprised of a plurality of individual strandsarranged in a bundle.
 6. An expansion joint for electrically connectingassociated ends of a pair of electrical conductors comprising, a pair ofspaced supports each adapted to be fixed to an associated one of saidelectrical conductors, a plurality of electrical leads having theiropposite ends fixed to said spaced supports with each end being fixed toan associated support on a given diameter, and means engaging androtating a central portion of each lead relative to both of its oppositeends to take up any slack therein caused by relative axial movement ofsaid supports to keep said leads within the confines of a theoreticalcylIndrical boundary extending between said supports and having saidgiven diameter.
 7. An expansion joint as set forth in claim 6 in whicheach of said pair of electrical conductors has a circular outline with adiameter equal to said given diameter and each of said supportscomprises a circular plate having an outside diameter also approximatelyequal to said given diameter.
 8. An expansion joint for electricallyconnecting associated ends of a pair of electrical conductorscomprising, a pair of spaced supports each adapted to be fixed to anassociated one of said electrical conductors, a plurality of electricalleads having their opposite ends fixed to said spaced supports with eachend being fixed to an associated support on a given diameter, and meansrotating a central portion of said leads to take up any slack thereincaused by relative movement of said supports to keep said leads withinthe confines of a theoretical cylindrical boundary extending betweensaid supports and having said given diameter, said rotating meanscomprising a central circular disc having an outside diameter equal tosaid given diameter and having the central portions of said leads fixedto the outer periphery thereof at spaced intervals and a spring deviceacting between at least one support and said central disc, said springdevice yieldingly rotating said central disc to thereby rotate thecentral portion of each lead to take up any slack therein while keepingsaid leads within said cylindrical boundary.
 9. An expansion joint forelectrically connecting associated ends of a pair of electricalconductors comprising, a pair of spaced supports each adapted to befixed to an associated one of said electrical conductors, a plurality ofelectrical leads having their opposite ends fixed to said spacedsupports with each end being fixed to an associated one of saidelectrical conductors, a plurality of electrical leads having theiropposite ends fixed to said spaced supports with each end being fixed toan associated support on a given diameter, and means rotating a centralportion of said leads to take up any slack therein caused by relativemovement of said supports to keep said leads within the confines of atheoretical cylindrical boundary extending between said supports andhaving said given diameter, each of said supports having a circularperipheral outline and a diameter equal to said given diameter, witheach end of said leads being fixed to an associated support about itsperipheral outline to define said expansion joint having a roughlycylindrical configuration of constant diameter which corresponds to saidtheoretical cylindrical boundary, said rotating means comprising acentral circular disc having an outside diameter equal to said givendiameter and having the central portions of said leads fixed to theouter periphery thereof at spaced intervals and a spring device actingbetween at least one support and said central disc, said spring deviceyieldingly rotating said central disc to thereby rotate the centralportion of each lead to take up any slack therein while maintaining saidcylindrical configuration of said expansion joint substantially intact.10. An expansion joint as set forth in claim 9 in which said rotatingmeans further comprises a rod having one end portion fixed to one ofsaid supports and its opposite end portion supported by the othersupport for sliding movement relative thereto, said central disc beingrotatably supported by said rod and said spring device acting betweensaid rod and central disc to rotate said disc and said central portionof each lead.
 11. An expansion joint as set forth in claim 10 in whichsaid rod comprises a right circular cylindrical rod and said centraldisc has a right circular cylindrical inside surface extending throughthe center thereof which defines an opening for receiving said rod, saidcylindrical surface supporting and enabling free rotation of saidcentral disc about said rod.
 12. An expansion joint as set forth inclaim 10 in which said spring device comprises a torsion spring and eachof said electrical leads is comprised of a plurality of individualstrands arranged in a bundle.
 13. An electrical power transmissionsystem comprising; an outer protective conduit; a plurality of elongatedelectrical conductors supported in electrically insulated relationwithin said conduit; and an expansion joint for electrically connectingassociated ends of an adjacent pair of said elongated conductorssupported within said conduit; said expansion joint comprising, a pairof spaced supports each fixed to an associated one of said electricalconductors, a plurality of electrical leads having their opposite endsfixed to said spaced supports with each end being fixed to an associatedsupport on a given diameter, and means engaging and rotating a centralportion of each lead relative to both of its opposite ends to take upany slack therein caused by relative axial movement of said supports tokeep said leads within the confines of a theoretical cylindricalboundary extending between said supports and having said given diameter.14. A system as set forth in claim 13 and further comprising a pluralityof disclike electrical insulating spacers each fixed concentricallyaround an associated electrical conductor and each supporting anassociated conductor within said conduit.
 15. A system as set forth inclaim 14 in which each of said spacers has a plurality of passagesextending therethrough and said system further comprising an electricalinsulating fluid contained within said conduit under pressure andfilling the volume between each electrical conductor and expansion jointand said conduit, said electrical insulating fluid being free to flowthrough said passages to provide improved insulation and cooling alongthe full length of each electrical conductor and any associatedexpansion joint.
 16. A system as set forth in claim 13 in which each ofsaid pair of electrical conductors has a circular outline with adiameter equal to said given diameter and each of said supportscomprises a circular plate having an outside diameter also approximatelyequal to said given diameter.
 17. An electrical power transmissionsystem comprising; an outer protective conduit; a plurality of elongatedelectrical conductors supported in electrically insulated relationwithin said conduit; and an expansion joint for electrically connectingassociated ends of an adjacent pair of said elongated conductorssupported within said conduit; said expansion joint comprising; a pairof spaced supports each fixed to an associated one of said electricalconductors, a plurality of electrical leads having their opposite endsfixed to said spaced supports with each end being fixed to an associatedsupport on a given diameter, and means rotating a central portion ofsaid leads to take up any slack therein caused by relative movement ofsaid supports to keep said leads within the confines of a theoreticalcylindrical boundary extending between said supports and having saidgiven diameter, each of said supports having a circular peripheraloutline and a diameter equal to said given diameter with each end ofsaid leads being fixed to an associated support about its peripheraloutline to define said expansion joint having a roughly cylindricalconfiguration of constant diameter which corresponds to said theoreticalcylindrical boundary, said rotating means comprising a central circulardisc having an outside diameter equal to said given diameter and havingthe central portions of said leads fixed to the outer periphery thereofat spaced intervals and a spring device acting between at least onesupport and said central disc, said spring device yieldingly rotatingsaid central disc to thereby rotate the central portion of each lead totake up any slack therein while maintaining said cylindricalconfiguration of said expansion joint substantially intact.
 18. A systemas set forth in claim 17 in which said rotating means compriseS a rodhaving one end portion fixed to one of said supports and its oppositeend portion supported by the other support for sliding movement relativethereto, said central disc being rotatably supported by said rod andsaid spring device acting between said rod and central disc to rotatesaid disc and said central portion of each lead.
 19. A system as setforth in claim 18 in which said rod comprises a right circularcylindrical rod and said central disc has a right circular cylindricalsurface through the center thereof which defines an opening forreceiving said rod, said cylindrical surface supporting and enablingfree rotation of said central disc about said rod.
 20. A system as setforth in claim 18 in which said spring device comprises a torsion springand each of said electrical leads is comprised of a plurality ofindividual strands arranged in a bundle.